Iron ore concentrate, finely divided iron ore in powder form, from which undesired components of the ore have been removed, is mixed with water in a preparation plant in order subsequently to be processed in a pelletising plant.
The ore concentrate is dewatered in the pelletising plant and mixed with various additives and binding agents, and rolled to pellets. The pellets are dried in a drying arrangement and heated in a compartment such that the pellets are oxidised and sintered, caused to melt together, one by one, to form final pellets, which maintain their shape during further transport. A cooling of the pellets subsequently takes pace in a cooling arrangement. The pellets are now ready and can be transported onwards to the locations at which the ore is to be further refined.
The use of an arrangement comprising an inlet connected to the compartment for introduction of a medium through the inlet and into the compartment is previously known. A combustion arrangement for heating the medium is arranged in the inlet. The combustion arrangement comprises fuel that, when the arrangement is in use, is ignited and combusted. Combustion heat is developed during the combustion of the fuel, which heat is transferred to the medium that is present at the combustion arrangement in the inlet and that passes through the inlet on its way to the compartment.
The heating of the pellets in a compartment is a very critical step in the processing of the pellets and requires a relatively high temperature in order to obtain a good result, in order for the pellets to be durable. There is a desire to secure, or even to increase, the heat of the medium in order to improve the sintering.
The heating, the sintering, the oxidation, of the pellets results in conversion of magnetite to haematite, having NOx as a waste product. NOx becomes present in the medium, which has, after the sintering, completed its task and is to be replaced by new, hot medium. NOx is harmful to the environment and it is therefore desirable that the sintering give rise to as little NOx as possible.
The introduction of cold air that is heated in order to be used as the hot medium gives a good reduction in NOx level, but brings with it the result that the energy consumption becomes high.